Behringer EP2500 Clip light Channel 2 stays on & heatsink HOT!

In the first place, the LM311 is NOT an op-amp but a comparator.



Most chips will either show a burned spot or raised spot in the middle OR there will be "greasy" looking traces on the sides of the chip near the middle when fried.



If the LM311 is fried, you have a MAJOR number of other things that would be fried as well. T45, T46 and/or the opposite side T36, T37 would likely be gone. D79 and/or D59.



The section with T15 and T17 might also have damage as well as the eight transistors that are in two groups in parallel. D78 would be suspect as well as the gate resistors for the switchers.



This amp has an odd design and appears to be a hybrid of class D switching amp (the LM311 comparator driven parts and a linear section with all those parallel transistors.



I can almost guarantee that if the power MOSFET switchers have failed that the driver transistors I have mention as well as the LM311 are gonzo. The circuitry is similar to that they use in the power supplies in the PMP series powered mixers.



The only thing I can recommend is to check EACH component that are in the line of fire before powering the unit again and DO use the limiting light bulb trick. In the first place, the LM311 is NOT an op-amp but a comparator.

Most chips will either show a burned spot or raised spot in the middle OR there will be "greasy" looking traces on the sides of the chip near the middle when fried.

If the LM311 is fried, you have a MAJOR number of other things that would be fried as well. T45, T46 and/or the opposite side T36, T37 would likely be gone. D79 and/or D59.

The section with T15 and T17 might also have damage as well as the eight transistors that are in two groups in parallel. D78 would be suspect as well as the gate resistors for the switchers.

This amp has an odd design and appears to be a hybrid of class D switching amp (the LM311 comparator driven parts and a linear section with all those parallel transistors.

I can almost guarantee that if the power MOSFET switchers have failed that the driver transistors I have mention as well as the LM311 are gonzo. The circuitry is similar to that they use in the power supplies in the PMP series powered mixers.

The only thing I can recommend is to check EACH component that are in the line of fire before powering the unit again and DO use the limiting light bulb trick.

Hi Freddy,
I'm repairing a Behringer EP2500 right now (i buy defective amps, Crown, Behringer, Craaft, Crest Audio, ... on Ebay, fix them and sell them back), and they are NOT class D (digital signal on the output transistors with an LC filter on the output).
This is what they call a class A/AB, invented & patented by CROWN in 1974. (google for it, you'll find plenty of info).
It's a little ackward design, i agree, but it has a lot of advantages compared to the "normal" class AB. And yes they are complicated to work on.:

* in this design the transistor only "sees" the peak voltage where in the AB design it "sees" TWICE the peak voltage, resulting in cheaper power components. (a 150V / 15A / 150W transistor is cheaper than a 250V / 15A / 250W transistor)

* Where the "normal" AB design uses two sec. coils on the transformer (symmetric power supply) with center tap to GND, and with each pos. or neg. alternance only 1 coil is doing the work, the A/AB design uses a MONORAIL power supply with FLOATING GND (set by the output transistors), this means that the transformer sec. coil is used constantly for pos. as for the neg. alternance, by balancing the voltage up and down (it follows the signal). In other words, with a 80V single supply, you can create a output swing of +80V and -80V !! Resulting in a smaller / lighter transformer ... With a AB design you'll need a 160V power supply with center tap. This is why QSC, Crown & Craaft can fit a 2x2000W FULLY ANALOG amp in a 2 units 19" rack. Working with SMPS is another thing, lighter, but more complex.

To be correct the EP2500 is a class G, this is a class AB (or A/AB) with a sec. power rail that comes in action when a certain output level is reached, this way they can limit the heat dissipation and use a smaller heatsink.
A class H would be better, this uses the same technology as a class G, but instead of jumping to a higher voltage, it follows the signal a few volts above the output, this reduces the dissipation even more, but uses more power components.

But like i said, they're tricky to work on, for example: when measuring the power rails, they have the signal superposed on it ... and THINK first where you're connecting the GND of your scope probe in the circuit, because the GND IS NOT THE GND like in a "normal" AB design !! The power supply HAS NO GND.

Compared to the QSC RMX2450 they are ALLMOST the same, main differences are:

* QSC uses a NE5532 opamp, Behringer uses a LM4580, the NE5532 has better specs (SN ratio...)

* QSC uses 2N3904 & 3906 transisors, Behringer MPSA06 & A56, not much difference here.

* IMPORTANT, And this is where one day you'll thank QSC for, because it's only 7 components that WILL make the difference. QSC uses a "crowbar" on the output, for DC protection (only the RMX2450), this will blow the 25A fuse and keep the speakers safe, Behringer has NO PROTECTION !! (bye bye amp & bye bye speakers) I don't understand why Behringer left this out, it's so important and it costs NOTHING, i recommend building it youreself and implement it in the amp (7 components ... pleaeaease !!)
For schematics, QSC has EVERYTHING on their support webpage, for Behringer, use google. Hi Freddy, I'm repairing a Behringer EP2500 right now (i buy defective amps, Crown, Behringer, Craaft, Crest Audio, ... on Ebay, fix them and sell them back), and they are NOT class D (digital signal on the output transistors with an LC filter on the output). This is what they call a class A/AB, invented & patented by CROWN in 1974. (google for it, you'll find plenty of info). It's a little ackward design, i agree, but it has a lot of advantages compared to the "normal" class AB. And yes they are complicated to work on.: * in this design the transistor only "sees" the peak voltage where in the AB design it "sees" TWICE the peak voltage, resulting in cheaper power components. (a 150V / 15A / 150W transistor is cheaper than a 250V / 15A / 250W transistor) * Where the "normal" AB design uses two sec. coils on the transformer (symmetric power supply) with center tap to GND, and with each pos. or neg. alternance only 1 coil is doing the work, the A/AB design uses a MONORAIL power supply with FLOATING GND (set by the output transistors), this means that the transformer sec. coil is used constantly for pos. as for the neg. alternance, by balancing the voltage up and down (it follows the signal). In other words, with a 80V single supply, you can create a output swing of +80V and -80V !! Resulting in a smaller / lighter transformer ... With a AB design you'll need a 160V power supply with center tap. This is why QSC, Crown & Craaft can fit a 2x2000W FULLY ANALOG amp in a 2 units 19" rack. Working with SMPS is another thing, lighter, but more complex. To be correct the EP2500 is a class G, this is a class AB (or A/AB) with a sec. power rail that comes in action when a certain output level is reached, this way they can limit the heat dissipation and use a smaller heatsink. A class H would be better, this uses the same technology as a class G, but instead of jumping to a higher voltage, it follows the signal a few volts above the output, this reduces the dissipation even more, but uses more power components. But like i said, they're tricky to work on, for example: when measuring the power rails, they have the signal superposed on it ... and THINK first where you're connecting the GND of your scope probe in the circuit, because the GND IS NOT THE GND like in a "normal" AB design !! The power supply HAS NO GND. Compared to the QSC RMX2450 they are ALLMOST the same, main differences are: * QSC uses a NE5532 opamp, Behringer uses a LM4580, the NE5532 has better specs (SN ratio...) * QSC uses 2N3904 & 3906 transisors, Behringer MPSA06 & A56, not much difference here. * IMPORTANT, And this is where one day you'll thank QSC for, because it's only 7 components that WILL make the difference. QSC uses a "crowbar" on the output, for DC protection (only the RMX2450), this will blow the 25A fuse and keep the speakers safe, Behringer has NO PROTECTION !! (bye bye amp & bye bye speakers) I don't understand why Behringer left this out, it's so important and it costs NOTHING, i recommend building it youreself and implement it in the amp (7 components ... pleaeaease !!) For schematics, QSC has EVERYTHING on their support webpage, for Behringer, use google.